The utilization of microbiocides for the control and destruction of microorganisms has long been a matter of great importance and has taken on even more importance as a result of the growing awareness of the expense and problems caused by the uncontrolled growth of microorganisms. Such microbiocides are generally referred to as antimicrobials, antiseptics, disinfectants, sanitizers, germicides, bactericides, antiviral agents, algaecides, slimicides, antifouling agents and preservatives.
Microbiocides are used in surface disinfection in private homes as well as in commercial, institutional and public buildings, in communal toilet facilities and swimming pool and changing rooms, in food processing plants and food service facilities and in industrial and building recirculating cooling water systems. They are used to treat many types of surfaces such as walls, floors, paintwork, lavatories, sinks and bench tops. Microbiocides are also applied to marine construction including buildings, off-shore drilling rigs and marine vessels as components of antifouling marine coatings. Microbiocides are also applied to human and animal skin and other surfaces.
The microbiocides are generally effective only as long as they persist on the substrate to which they are applied. Consequently, frequent application is necessary.
The principles of antimicrobial activity have been enunciated by J. F. Gardiner ("Disinfection, Sterilization, and Preservation", edited by S. S. Block, 2nd Edition, Lea & Febiger, Philadelphia, Pa., 1977, Chapter 43, p. 883). Antimicrobial activity occurs when a physical or chemical agent interacts with a component of the organism which is essential to its structure or metabolism. The target may be a cell constituent or a single enzyme.
Effective contact between the microbiocide and the microorganism is an essential prerequisite for antimicrobial action. It is influenced by physical barriers and by soluble or particulate substances in the environment which inactivate or reduce the concentration of the microbiocide by adsorption. Adsorption or uptake of the latter by microorganisms depends on the bonds which are formed between the molecules of the microbiocide and the cell surface, e.g. van der Waals bonds, hydrogen bonds, ionic bonds and covalent bonds. Notwithstanding the nature of the ultimate bonding, effective contact is necessary before the penetration of chemicals to the cell membrane or cytoplasm can occur.
Microorganisms are the smallest living creatures, with the shortest generation times and the greatest population densities. They possess a unique ability to survive in different and oftentimes hostile environments and to reinvade, grow, reproduce and reinfect an area which has only newly been freed of contamination. Since the growth rate of microbial populations is generally exponential, a reduction in a given population is not adequate. Total sterilization, disinfection and/or sanitation is necessary, since an environment cannot be "practically sterile". Consequently, antimicrobial treatment must be immediately effective and frequent.
Pesticides, particularly insecticides, are utilized in the elimination of more complex organisms with longer life cycles and, generally, various stages of development, each of which may be susceptible to pesticidal action. The frequency of application of a pesticide to prevent reinfestation is many orders of magnitude less than that necessary in the case of a microbiocide. Further, pest elimination may only be necessary during certain seasons, e.g. during the period when the destructive stage of the insect's life cycle is generated or during the growth stage of a plant.
The modern development of controlled release pesticides, particularly insecticides, has resulted in extension of the duration between applications and thus increased the efficiency and economy of control in agricultural and non-agricultural applications.
The controlled release of insecticides has been achieved by their incorporation within a polymeric matrix, e.g. encapsulation wherein a pesticide is surrounded by an enveloping polymeric wall that permits escape through diffusion, permeation or degradation; dispersion of the pesticide in an elastomer or a plastic wherein the pesticide is released through leaching or diffusion; and the chemical combination of the pesticide with a polymer in such a manner that the appended pesticide slowly breaks off the polymeric backbone upon exposure to the pest infested environment, e.g by hydrolysis of the linkage.
In view of the need to obtain intimate, and in most cases, immediate, contact between a microorganism and a sufficient concentration of a microbiocide to have a lethal effect, the encapsulation, dispersion or chemical bonding of the latter within a polymeric matrix would not be expected to control the release of the toxic agent, while also providing for the speed and efficiency of action required to eliminate microorganism contamination. Consequently, the methods generally used for the controlled release of pesticides, including insecticides, fungicides and herbicides, would not be applicable to the effective controlled release of microbiocides. Further, the various approaches indicated above for the controlled release of pesticides failed to provide for adequate adhesion of the pesticide within the polymeric matrix to the substrate. This permitted the removal or transfer of the material from the substrate as a result of physical contact or atmospheric conditions.
The simultaneous development of adhesion to the substrate and controlled release characteristics, has recently been achieved by the discovery of compositions containing pesticides and moisture-reactive components which, on exposure to the atmosphere, undergo adhesion-promoting crosslinking reactions to form polymer networks which control pesticide release, while remaining strongly adherent to the substrate.
Surprisingly, it has now been found that the adherent, crosslinking sites which are generated due to the presence of the moisture-reactive components are capable of permitting the release of a microbiocide rapidly enough for effective elimination of a microorganism, while controlling and prolonging the duration of the release.